Electronic circuit

ABSTRACT

An electronic circuit includes: first through third transistors having a control terminal, first and second terminals; a first direct current path supplying a direct current having passed through between the first terminal and the second terminal of at least one of the second transistor and the third transistor to the second terminal of the transistor at former position compared to the transistor through which the direct current passed; a second direct current path that is different from the first direct current path and supplies a direct current having passed through between the first terminal and the second terminal of at least one of the second transistor and the third transistor to the second terminal of the transistor at former position compared to the transistor through which the direct current passed; and a common coupling point coupling the first direct current path and the second direct current path in common.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2010-214471, filed on Sep. 24,2010, the entire contents of which are incorporated herein by reference.

BACKGROUND

(i) Technical Field

The present invention relates to an electronic circuit, and inparticular, relates to a current reuse electronic circuit.

(ii) Related Art

There is known a current reuse electronic circuit using a latter DC(direct current) as a former DC in a multiple-stage electronic circuit.Japanese Patent Application Publication No. 2008-35083 (hereinafterreferred to as Document 1) discloses an art where a current reuseelectronic circuit is used as a doubler.

SUMMARY

The current reuse electronic circuit disclosed in Document 1 has atwo-stage transistor structure. For example, when the current reuseelectronic circuit is structured with three or more stage of transistorsin order to improve the performance of the electronic circuit, it isnecessary to reduce a voltage of each stage or increase a voltage of anelectrical power supply. However, when the voltage of each stage isreduced, the performance of the electronic circuit may be degraded. Itis necessary to prepare an electronic power supply having a high voltagein order to increase the voltage of the electrical power supply.

It is an object of the present invention to provide an electroniccircuit using low electrical power voltage and having high performance.

According to an aspect of the present invention, there is provided anelectronic circuit including: a first transistor having a controlterminal to which a signal is input, a first terminal, and a secondterminal; a second transistor having a control terminal coupled to thesecond terminal of the first transistor, a first terminal, and a secondterminal; a third transistor having a control terminal coupled to thesecond terminal of the second transistor, a first terminal and a secondterminal; a first direct current path supplying a direct current havingpassed through between the first terminal and the second terminal of atleast one of the second transistor and the third transistor to thesecond terminal of the transistor at former position compared to thetransistor through which the direct current passed; a second directcurrent path that is different from the first direct current path andsupplies a direct current having passed through between the firstterminal and the second terminal of at least one of the secondtransistor and the third transistor to the second terminal of thetransistor at former position compared to the transistor through whichthe direct current passed; and a common coupling point coupling thefirst direct current path and the second direct current path in common.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a circuit diagram of an electronic circuit inaccordance with a first comparative embodiment;

FIG. 1B illustrates a circuit diagram of the electronic circuit ingalvanically configuration;

FIG. 2A illustrates a circuit diagram of an electronic circuit inaccordance with a second comparative embodiment;

FIG. 2B illustrates a circuit diagram of the electronic circuit ingalvanically;

FIG. 3A illustrates a circuit diagram in accordance with a firstembodiment;

FIG. 3B illustrates a circuit diagram of the electronic circuit ingalvanically;

FIG. 4 illustrates a simulation result of a gain with respect tofrequency of the electronic circuit;

FIG. 5A illustrates a circuit diagram of an electronic circuit inaccordance with a second embodiment;

FIG. 5B illustrates a circuit diagram of the electronic circuit ingalvanically; and

FIG. 6 illustrates a circuit diagram of an electronic circuit inaccordance with a modified embodiment of the second embodiment.

DETAILED DESCRIPTION

A description will be given of a current reuse amplifier circuit withreference to a first comparative embodiment. FIG. 1A illustrates acircuit diagram of an electronic circuit in accordance with the firstcomparative embodiment. FIG. 1B illustrates a circuit diagram of theelectronic circuit in galvanically. As illustrated in FIG. 1A, anelectronic circuit 55 is a two-stage amplifier circuit having a firsttransistor T1 and a second transistor T2. A description will be given ofan example of an FET (Field Effect Transistor) acting as the firsttransistor T1 and the second transistor T2.

An inputting terminal Tin of the electronic circuit 55 is coupled to agate G1 (control terminal) of the first transistor T1. A source S1(first terminal) of the first transistor T1 is grounded via a capacitorC1 and a resistor R5. The capacitor C1 and the resistor R5 are coupledin parallel. The capacitor C1 grounds the source S1 in high frequency.The resistor R5 grounds the source S1 in galvanically and increases anelectrical potential of the source S1. Thus, the source S1 is groundedin galvanically and in high frequency. A drain D1 (second terminal) ofthe first transistor T1 is coupled to a gate G2 (control terminal) ofthe gate G2 of the second transistor T2 via a distributed parametertransmission lines L1 and L5.

A source S2 (first terminal) of the second transistor T2 is grounded viaa capacitor C2. The capacitor C2 grounds the source S2 in high frequencybut does not ground the source S2 in galvanically. A distributedparameter line L2 and a first resistor R1 are coupled in series betweena node N1 between the distributed parameter transmission lines L1 and L5and the source S2. The distributed parameter lines L1, L2 and L5 makeimpedance matching between the first transistor T1 and the secondtransistor T2. The first resistor R1 makes electrical potentialdifference between the source S2 and the gate G2 and determines thepotential applied to the gate G2. Further, the first resistor R1 makesresistance matching when making impedance matching between the firsttransistor T1 and the second transistor T2. The first resistor R1 may becoupled between the node N1 and the distributed parameter line L2. Thedrain D2 (second terminal) of the second transistor T2 is coupled to theoutputting terminal Tout. The direct voltage VDD is applied to the drainD2 of the second transistor T2 via a choke inductance such as a stab.

A signal from an inputting terminal Tin is input to the gate G1 of thetransistor T1, is amplified by the first transistor T1, and is outputfrom the drain D1. The signal amplified by the first transistor T1 isinput to the gate G2 of the second transistor T2, is amplified by thesecond transistor T2 and is output to the outputting terminal Tout fromthe drain D2.

The source S2 of the second transistor T2 is not grounded ingalvanically because of the capacitor C2. Therefore, as illustrated inFIG. 1B, the direct current from an electrical power supply applying thedirect voltage VDD passes through a direct current path 30 (illustratedin FIG. 1A) structured with the drain D2 of the second transistor T2,the source S2, the first resistor R1, the node N1, the drain D1 of thefirst transistor T1, the source S1 and the resistor R5. Thus, the directvoltage VDD is applied to the first transistor T1 and the secondtransistor T2 in series. The current from the electrical power supplyapplying the direct voltage VDD passes through the first transistor T1and the second transistor T2.

In FIG. 1A, a high frequency signal (a signal having a frequency atwhich the electronic circuit 55 acts as an amplifier) is transmittedthrough a high frequency path 20 from the drain D1 of the firsttransistor T1 to the gate G2 of the second transistor T2. The directcurrent passes through the direct current path 30 from the source S2 ofthe second transistor T2 to the drain D1 of the first transistor T1.Thus, the direct current path 30, of which at least a part is differentfrom the high frequency path 20, applies the direct voltage to thesource S2 and the drain D2 of the second transistor T2.

It is therefore possible to reduce consumption current compared to anamplifier circuit supplying a current to each stage transistorindependently. An identical voltage is applied to the first transistorT1 and the second transistor T2 when a gate width of the firsttransistor T1 is the same as that of the second transistor T2 and theresistance of the resistor R1 is the same as that of the resistor R5. Itis therefore possible to increase a gain of the current reuse amplifiercircuit and to downsize the current reuse amplifier circuit.

The number of the stage of transistor may be increased as a method forimproving the performance of the current reuse circuit in accordancewith the first comparative embodiment. For example, the number of thestage of the transistor may be increased to three from two whenincreasing the gain of the amplifier circuit. A second comparativeembodiment is a current reuse circuit having a three-stage transistorstructure.

FIG. 2A illustrates a circuit diagram of an electronic circuit inaccordance with the second comparative embodiment. FIG. 2B illustrates acircuit diagram of the electronic circuit in galvanically. Asillustrated in FIG. 2A, in an electronic circuit 56, the drain D2 of thesecond transistor T2 is coupled to the gate G3 (control terminal) of thethird transistor T3 via the distributed parameter transmission lines L4and L6.

The source S3 (first terminal) of the third transistor T3 is groundedvia the capacitor C3. The capacitor C3 grounds the source S2 in highfrequency, but does not ground the source S2 in galvanically. Thedistributed parameter line L3 and the second resistor R2 are coupled inseries between the node N2 between the distributed parameter lines L4and L6 and the source S3. The distributed parameter lines L3, L4 and L6make impedance matching between the second transistor T2 and the thirdtransistor T3. The second resistor R2 makes potential difference betweenthe source S3 and the gate G3, and determines potential applied to thegate G3. The drain D3 of the third transistor T3 is coupled to theoutputting terminal Tout. The direct voltage VDD is applied to the drainD3 of the third transistor T3 via a choke inductor such as a stab. Theother structure is the same as FIG. 1A. Therefore, explanation of theother structure is omitted.

As illustrated in FIG. 2B, the direct current from the electrical powersupply applying the direct voltage VDD passes through the drain D3 ofthe third transistor T3, the source S3, the second resistor R2, the nodeN2, the drain D2 of the second transistor T2, the source S2, the firstresistor R1, the node N1 the drain D1 of the first transistor T1, thesource S1 and the resistor R5. Thus, the direct voltage VDD is appliedto the third transistor T3 from the first transistor T1 in series. Thecurrent from the electrical power supply applying the direct voltage VDDpasses through from the first transistor T1 to the third transistor T3.

In accordance with the second comparative embodiment, the voltage ofeach transistor may be reduced when the direct voltage VDD that is thesame as the first comparative embodiment is applied. Therefore, theperformance of the electronic circuit 56 is not improved. For example,the gain or linearity performance is not increased. On the other hand,the direct voltage VDD becomes 1.5 times as the first comparativeembodiment, when the voltage of each transistor is the same as the firstcomparative embodiment in order to improve the performance. In thiscase, it is prepare a high electrical power supply. And so, adescription will be given of embodiments of an electronic circuit usinglow electrical power voltage and having high performance.

First Embodiment

FIG. 3A illustrates a circuit diagram of an electronic circuit inaccordance with a first embodiment. FIG. 3B illustrates a circuitdiagram of an electronic circuit in galvanically. In an electroniccircuit 50, a distributed parameter line L4, a capacitor C5 and adistributed parameter line L6 are coupled to in series between the drainD2 of the second transistor T2 and the gate G3 of the transistor T3. Thenode N2 between the distributed parameter line L4 and the capacitor C5is grounded via the distributed parameter line L7 and the capacitor C4.The direct voltage VDD is applied to a node between the distributedparameter line L7 and the capacitor C4 for cutting direct current via achoke inductor such as a stab. The distributed parameter line L3 and thesecond resistor R2 are coupled in series between the node N1 and thesource S3. A distributed parameter line L8 is coupled between the thirdnode N3 between the distributed parameter line L3 and the secondresistor R2 and a node between the capacitor C5 and the distributedparameter line L6. The distributed parameter lines L4, L6, L7 and L8 andthe capacitor C5 make impedance matching between the second transistorT2 and the third transistor T3. The capacitor C5 transmits a highfrequency signal and cuts a direct current.

The source S3 of the third transistor T3 is grounded via the capacitorC3. The capacitor C3 grounds the source S3 in high frequency, but doesnot ground the source S3 in galvanically. The distributed parameterlines L6 and L8 and the second resistor R2 are coupled in series betweenthe gate G3 of the third transistor T3 and the source S3 of the thirdtransistor T3. The distributed parameter lines L3 and L8 are coupled inparallel at the node N3. The second resistor R2 makes potentialdifference between the source S3 and the gate G3, and determinespotential applied to the gate G3. Resistors having resistance that isthe same as the second resistor R2 may be respectively coupled betweenthe node N1 and the distributed parameter line L3 and between thedistributed parameter lines L6 and L8. The direct voltage VDD is appliedto the drain D3 of the third transistor T3 via a choke inductor such asa stab. The other structure is the same as FIG. 1A. Therefore,explanation of the other structure is omitted.

A signal input from the inputting terminal Tin is input to the gate G1of the first transistor T1, is amplified by the first transistor T1. Thesignal amplified by the first transistor T1 is output from the drain D1.The signal amplified by the first transistor T1 is input to the gate G2of the second transistor T2, is amplified by the second transistor T2.The signal amplified by the second transistor T2 is output from thedrain D2. The signal amplified by the second transistor T2 is input tothe gate G3 of the third transistor T3, is amplified by the thirdtransistor T3. The signal amplified by the third transistor T3 is outputto the outputting terminal Tout from the drain D3. Thus, the electroniccircuit 50 acts as a three-stage amplifier circuit.

On the other hand, as illustrated in FIG. 3A and FIG. 3B, the directcurrent from the electrical power supply applying the direct voltage VDDpasses through a first direct current path 31. The first direct currentpath 31 is structured with the drain D2 of the second transistor T2, thesource S2, the first resistor R1, the node N1, the drain D1 of the firsttransistor T1, the source S1 and the resistor R5. Further, directcurrent from the electrical power supply applying the direct voltage VDDpasses through a second direct current path 32. The second directcurrent path 32 is structured with the drain D3 of the third transistorT3, the source S3, the second resistor R2, the node N1, the drain D1 ofthe first transistor T1, the source S1 and the resistor R5. Thus, thedirect voltage VDD is applied to the first transistor T1 and the secondtransistor T2 in series, and is applied to the first transistor T1 andthe third transistor T3 in series. The node N1 is a common couplingpoint of the first direct current path 31 and the second direct currentpath 32. Thus, the first direct current path 31 and the second directcurrent path 32 are coupled in parallel, because the common couplingpoint is provided. It is therefore possible to reduce the voltage of thedirect voltage VDD.

In accordance with the first embodiment, in FIG. 3A, the gate G2 of thesecond transistor T2 is coupled to the drain D1 of the first transistorT1 in high frequency. A high frequency signal is transmitted via a firsthigh frequency path 21 from the drain D1 of the first transistor T1 tothe gate G2 of the second transistor T2. A direct current passes throughthe first direct current path 31 from the source S2 of the secondtransistor T2 to the drain D1 of the first transistor T1. Thus, thefirst direct current path 31 of which at least a part is different fromthe first high frequency path 21 applies a direct voltage to the sourceS2 and the drain D2 of the second transistor T2. Further, the gate G3 ofthe third transistor T3 and the drain D2 of the second transistor T2 arecoupled in high frequency. A high frequency signal passes through asecond high frequency path 22 from the drain D2 of the second transistorT2 to the gate G3 of the third transistor T3. The direct current passesthrough the second direct current path 32 from the source S3 of thethird transistor T3 to the drain D1 of the first transistor T1. Thesecond direct current path 32 of which at least a part is different fromthe first high frequency path 21, the second high frequency path 22 andthe first direct current path 31 applies a direct voltage to the sourceS3 and the drain D3 of the third transistor T3.

The first direct current path 31 supplies a direct current having passedthrough between the source and the drain of at least one of the secondtransistor T2 and the third transistor T3 to the drain of the transistorat former position compared to the transistor through which the directcurrent passed. The second direct current path 32 supplies a directcurrent having passed through between the source and the drain of atleast one of the second transistor T2 and the third transistor T3 to thedrain of the transistor at former position compared to the transistorthorough which the direct current passed. The second direct current path32 is different from the first direct current path 31. Further, thecommon coupling point (the node N1) couples the first direct currentpath 31 and the second direct current path 32 in common.

As mentioned above, two-stage transistors are coupled between theelectrical power supply and the ground in galvanically. Therefore, theamplification of three-stage transistor is possible with the directvoltage VDD that is the same as the first comparative embodiment. Evenif low electrical power voltages used, high performance can be obtained.

In accordance with the first embodiment, the first direct current path31 couples the node N1 in the first high frequency path 21 and thesource S2 of the second transistor T2. The second direct current path 32couples the node N1 and the source S3 of the third transistor T3. Thedrain D2 of the second transistor T2 is not coupled to the gate G3 ofthe third transistor T3 in galvanically. The source S2 of the secondtransistor T2 is not grounded in galvanically, but is grounded in highfrequency. The direct voltage VDD is applied to the drain D2 of thesecond transistor T2. The source S3 of the third transistor T3 is notgrounded in galvanically but is grounded in high frequency. The directvoltage VDD is applied to the drain D3 of the third transistor T3.

The common coupling point (the node N1) is coupled to the drain D1 ofthe first transistor T1. The first direct current path 31 includes apath coupling between the common coupling point (the node N1) and thesource S2 of the second transistor T2. The second direct current path 32includes a path coupling between the common coupling point (the node N1)and the source S3 of the third transistor T3.

Thus, the second transistor T2 and the third transistor T3 are coupledin parallel in galvanically. Three transistors are coupled in highfrequency. Thus, a current having passed though the second transistor T2and the third transistor T3 passes through the first transistor T1.Therefore, the gate width of the first transistor T1 is larger than thatof the second transistor T2 and the third transistor T3. It is thereforepossible to reduce noise factor (NF) because the gate width of the firsttransistor T1 at first stage is increased.

For example, in order to apply an identical voltage to each transistor,it is necessary that the gate width of the second transistor T2 is thesame as that of the third transistor T3, and the gate width of the firsttransistor T1 is two times as the gate width of the second transistor T2and the third transistor T3. In this case, the resistance of theresistor R1 is the same as that of the resistor R2. The resistance ofthe resistor R5 is half of the resistors R1 and R2.

Further, in accordance with the first embodiment, the first resistor R1is coupled in the first direct current path 31 in series, and the secondresistor R2 is coupled in the second direct current path 32. The firstresistor R1 determines potential difference between the source S2 of thesecond transistor T2 and the gate G2 of the second transistor T2 so thata predetermined potential is determined at the gate G2 of the secondtransistor T2. The second resistor R2 makes potential difference betweenthe source S3 of the third transistor T3 and the gate G3 of the thirdtransistor T3, and determines potential applied on the gate G3 of thethird transistor T3. Thus, potential of each transistor can bedetermined.

Further, in accordance with the first embodiment, one end of thedistributed parameter line L1 is coupled to the drain D1 of the firsttransistor T1, and the other of the distributed parameter line L1 iscoupled to the node N1. The distributed parameter line L2 is coupled tothe first resistor R1 in series between the node N1 and the source S2 ofthe second transistor T2. The distributed parameter line L3 is coupledto the second resistor R2 in series between the node N1 and the sourceS3 of the third transistor T3. That is, the distributed parameter lineL1 (first distributed parameter line) is provided in series with thefirst resistor R1 in the first direct current path 31. The distributedparameter line L2 (second distributed parameter line) is provided inseries with the second resistor R2 in the second direct current path 32.

One end of the distributed parameter line L4 is coupled to the drain D2of the second transistor T2. The other of the distributed parameter lineL4 is coupled to the node N2. One end of the distributed parameter lineL6 is coupled to the gate G3 of the third transistor T3. The other ofthe distributed parameter line L6 is coupled to the node N2 via thecapacitor C5. One end of the distributed parameter line L7 is coupled tothe node N2. The other of the distributed parameter line L7 is coupledto the direct voltage VDD. The distributed parameter line L8 is coupledin parallel with the second resistor R2 between a node between thecapacitor C5 and the distributed parameter line L6 and the source S3 ofthe third transistor T3.

The distributed parameter line L1 and the distributed parameter line L5make impedance matching between the drain D1 of the first transistor T1and the gate G2 of the second transistor T2. The distributed parameterline L2 and the distributed parameter line L3 act as an open stabbetween the first transistor T1 and the second transistor T2 and makeimpedance matching between the first transistor T1 and the secondtransistor T2.

The distributed parameter line L4, the distributed parameter line L6 andthe capacitor C5 make impedance matching between the drain D2 of thesecond transistor T2 and the gate G3 of the third transistor T3. Thedistributed parameter line L7 and the distributed parameter line L8 actas an open stab between the second transistor T2 and the thirdtransistor T3, and make impedance matching between the second transistorT2 and the third transistor T3.

Therefore, the impedance can be matched between the first transistor T1and the second transistor T2 and between the second transistor T2 andthe third transistor T3.

The capacitor C5 is provided between the drain D2 of the secondtransistor T2 and the gate G3 of the third transistor T3. One end of abias path is coupled to the second direct current path 32. The other endof the bias path is coupled to between the capacitor C5 and the gate G3of the third transistor T3. The capacitor C5 in galvanically isolatesthe drain D2 of the second transistor T2 from the gate G3 of the thirdtransistor T3. The second direct current path 32 applies a directvoltage to the gate G3 of the third transistor T3 via the bias path.

FIG. 4 illustrates a result of a simulation of a gain with respect to afrequency of the electronic circuit in accordance with the firstembodiment. The transistors T1 through T3 are a HEMT (High ElectronMobility Transistor) having gate length of 0.1 μm, an electron supplylayer made of AlGaAs, and an electron transit layer made of GaAs. Table1 shows a gate width W of each transistor, a resistance of eachresistor, capacitance of each capacitor, and size (length L and width W)of each distributed parameter line. A substrate of a distributedparameter circuit was made of GaAs and had thickness of 250 μm. Thedirect voltage VDD was 5V.

TABLE 1 T1 T2 T3 W μm 640 320 320 R1 R2 R5 Ω 4.8 4.8 2.4 C1 C2 C3 C4 C5pF 7 3 11.8 12 0.6 L1 L2 L3 L4 L5 L6 L7 L μm 320 600 1800 460 50 50 750W μm  20  20  20  20 20 20  20

As illustrated in FIG. 4, in the first embodiment, the gain (S21) in afrequency range from 17 GHz to 31 GHz exceeds 20 dB. For example, whenthe frequency is 24 GHz, the gain is 21.5 dB. When the frequency is 30GHz, the gain is 20.6 dB. The gain was 15 dB at a maximum, when asimulation was performed with use of the structure of the firstcomparative embodiment. Thus, in accordance with the first embodiment,the gain is increased compared to the first comparative embodiment.

Second Embodiment

FIG. 5A illustrates a circuit diagram of an electronic circuit inaccordance with a second embodiment. FIG. 5B illustrates a circuitdiagram of the electronic circuit in galvanically. In an electroniccircuit 52, the distributed parameter line L1, the capacitor C6 and thedistributed parameter line L5 are coupled in series between the drain D1of the first transistor T1 and the gate G2 of the second transistor T2.A node between the capacitor C6 and the distributed parameter line L5 isgrounded via the resistor R7. The distributed parameter line L3 iscoupled between the node N4 between the distributed parameter line L2and the first resistor R1 and the node N2 between the distributedparameter line L4 and the distributed parameter line L6. In FIG. 5B, theresistor R7 is grounded in galvanically. The distributed parameter linesL1, L2 and L5 and the capacitor C6 make impedance matching between thefirst transistor T1 and the second transistor T2. The capacitor C6transmits a high frequency signal and cuts a direct current. The sourceS2 of the second transistor T2 is grounded via the resistor R6 and thecapacitor C2. The source S2 is grounded in galvanically and in highfrequency.

The distributed parameter line L4 and the distributed parameter line L6are coupled in series between the drain D2 of the second transistor T2and the gate G3 of the third transistor T3. The distributed parameterlines L3, L4 and L6 make impedance matching between the secondtransistor T2 and the third transistor T3. The source S3 of the thirdtransistor T3 is grounded via the capacitor C3. The capacitor C3 groundsthe source S3 in high frequency but does not ground the source S3.

The distributed parameter line L2 and the first resistor R1 are coupledin series between the node N1 between the distributed parameter line L1and the capacitor C6 and the source S3 of the third transistor T3. Thedistributed parameter line L3 and the first resistor R1 are coupled inseries between the node N2 between the distributed parameter line L4 andthe distributed parameter line L6 and the source S3 of the thirdtransistor T3. The distributed parameter line L2 and the distributedparameter line L3 are coupled in parallel at the node N4. A resistorhaving the same resistance as the first resistor R1 may be coupledbetween the node N1 and the distributed parameter line L2 and betweenthe node N2 and the distributed parameter line L3. The direct voltageVDD is applied to the drain D3 of the third transistor T3 via a chokeinductor such as a stab. The other structure is the same as FIG. 1A.Therefore, explanation of the other structure is omitted.

A signal input from the inputting terminal Tin is input to the gate G1of the first transistor T1, is amplified by the first transistor T1, andis output from the drain D1. The signal amplified by the firsttransistor T1 is input to the gate G2 of the second transistor T2, isamplified by the second transistor T2, and is output from the drain D2.The signal amplified by the second transistor T2 is input to the gate G3of the third transistor T3, is amplified by the third transistor T3, andis output to the outputting terminal Tout from the drain D3. Thus, theelectronic circuit 52 acts as a three-stage amplifier circuit.

On the other hand, as illustrated in FIG. 5B, the direct current fromthe electrical power supply applying the direct voltage VDD passes thesecond direct current path 32 illustrated in FIG. 5A structured with thedrain D3 of the third transistor T3, the source S3, the first resistorR1, the drain D1 of the first transistor T1, the source S1 and theresistor R5. Further, the direct current from the electrical powersupply applying the direct voltage VDD passes through the first directcurrent path 31 illustrated in FIG. 5A structured with the drain D3 ofthe third transistor T3, the source S3, the first resistor R1, the drainD2 of the second transistor T2, the source S2, and the resistor R6.Thus, the direct voltage VDD is applied to the first transistor T1 andthe third transistor T3 in series, and is applied to the secondtransistor T2 and the third transistor T3 in series. The node N4 is acommon coupling point between the first direct current path 31 and thesecond direct current path 32. The first direct current path 31 and thesecond direct current path 32 are coupled in parallel because the commoncoupling point is provided. It is therefore possible to reduce thedirect voltage VDD.

In accordance with the second embodiment, in FIG. 5A, the first highfrequency path 21 couples the gate G2 of the second transistor T2 andthe drain D1 of the first transistor T1 in high frequency. A highfrequency signal is transmitted from the drain D1 of the firsttransistor T1 to the gate G2 of the second transistor T2 via the firsthigh frequency path 21. A direct current passes through the first directcurrent path 31 from the source S3 of the third transistor T3 to thedrain D2 of the second transistor T2. Thus, a direct voltage is appliedto the source S2 and the drain D2 of the second transistor T2 by thefirst direct current path 31 of which at least a part is different fromthe first high frequency path 21. Further, the second high frequencypath 22 couples the gate G3 of the third transistor T3 and the drain D2of the second transistor T2 in high frequency. A high frequency signalis transmitted from the drain D2 of the second transistor T2 to the gateG3 of the third transistor T3 via the second high frequency path 22. Adirect current passes through the second direct current path 32 from thesource S3 of the third transistor T3 to the drain D1 of the firsttransistor T1.

Thus, a direct voltage is applied to the source S3 and the drain D3 ofthe third transistor T3 by the second direct current path 32 of which atleast a part is different from the first high frequency path 21, thesecond high frequency path 22 and the first direct current path 31.

The first direct current path 31 supplies a direct current having passedthrough between the source and the drain of the third transistor T3 tothe drain of the second transistor T2. The second direct current path 32supplies a direct current having passed through between the source andthe drain of the third transistor T3 to the drain of the firsttransistor T1. Further, the common coupling point (the node N4) couplesthe first direct current path 31 and the second direct current path 32in common.

As mentioned above, two-stage transistors are coupled between theelectrical power supply and the ground in galvanically. Therefore, theamplification of three-stage transistor is possible with the directvoltage VDD that is the same as the first comparative embodiment. Evenif low electrical power voltage is used, high performance can beobtained.

In accordance with the second embodiment, the second direct current path32 couples the node N1 in the first high frequency path 21 and thesource S3 of the third transistor T3. The first direct current path 31couples the node N2 in the second high frequency path 22 and the sourceS3 of the third transistor T3. The drain D1 of the first transistor T1is not coupled to the gate G2 of the second transistor T2 ingalvanically. The source S3 of the third transistor T3 T2 is notgrounded in galvanically, but is grounded in high frequency. The sourceS3 of the third transistor T3 is not grounded in galvanically but isgrounded in high frequency. The direct voltage VDD is applied to thedrain D3 of the third transistor T3.

The common coupling point (the node N4) is coupled to the source S3 ofthe first transistor T3. The first direct current path 31 includes apath coupling between the common coupling point (the node N4) and thedrain D2 of the second transistor T2. The second direct current path 32includes a path coupling between the common coupling point (the node N4)and the drain D1 of the first transistor T2.

Thus, the first transistor T1 and the second transistor T2 are coupledin parallel in galvanically. Three transistors are coupled in highfrequency. Thus, a current having passed though the first transistor T1and the second transistor T2 passes through the third transistor T3.Therefore, the gate width of the third transistor T3 is larger than thatof the first transistor T1 and the second transistor T2. Accordingly,high output and low distortion are possible because the gate width ofthe third transistor T3 of last stage gets higher.

For example, in order to apply an identical voltage to each transistor,it is necessary that the width of the first transistor T1 is the same asthat of the second transistor, and the gate width of the thirdtransistor is two times as that of the first transistor T1 and thesecond transistor T2. In this case, the resistance of the resistor R5can be the same as that of the resistor R6. The resistance of the firstresistor R1 can be half of the resistors R5 and R6.

Further, the first resistor R1 is coupled between the common couplingpoint (the node N4) and the source S3 of the third transistor T3. Thus,electrical potential of each transistor can be determined.

Further, one end of the distributed parameter line L1 is coupled to thedrain D1 of the first transistor T1. The other of the distributedparameter line L1 is coupled to the node N1. The distributed parameterline L2 is coupled to the resistor R1 (second resistor) between the nodeN1 and the source S3 of the third transistor T3 in series. Thedistributed parameter line L2 (a second distributed parameter line) iscoupled between the node N4 and the drain D1 of the first transistor T1.One end of the distributed parameter line L5 is coupled to the gate G2of the second transistor T2. The other of the distributed parameter lineL5 is coupled to the node N1 via the capacitor C6. The distributedparameter line L3 is coupled to the first resistor R1 in series betweenthe node N2 and the source S3 of the third transistor T3. Thedistributed parameter line L3 (first distributed parameter line) iscoupled between the node N4 and the drain D2 of the second transistorT2. One end of the distributed parameter line L4 is coupled to the drainD2 of the second transistor T2. The other of the distributed parameterline L4 is coupled to the node N2. One end of the distributed parameterline L6 is coupled to the gate G3 of the third transistor T3. The otherof the distributed parameter line L6 is coupled to the node N2.

The distributed parameter line L1, the capacitor C6 and the distributedparameter line L5 make impedance matching between the drain D1 of thefirst transistor T1 and the gate G2 of the second transistor T2. Thedistributed parameter line L2 acts as an open stab between the firsttransistor T1 and the second transistor T2 and thereby makes impedancematching between the first transistor T1 and the second transistor T2.

The distributed parameter line L4 and the distributed parameter line L6make impedance matching between the drain D2 of the second transistor T2and the gate G3 of the third transistor T3. The distributed parameterline L3 acts as an open stab between the second transistor T2 and thethird transistor T3, and thereby make impedance matching between thesecond transistor T2 and the third transistor T3. It is thereforepossible to make impedance matching between the first transistor T1 andthe second transistor T2 and between the second transistor T2 and thethird transistor T3.

Further, the first direct current path 31 applies a direct bias to thegate G3 of the third transistor T3. It is therefore possible to apply adirect voltage to the gate G3 of the third transistor T3 via the firstdirect current path 31.

On the other hand, the capacitor C6 is coupled between the drain D1 ofthe first transistor T1 and the gate G2 of the second transistor T2. Thesecond direct current path 32 has a path coupling the capacitor C6 andthe drain D1 of the first transistor T1. A bias separated from thesecond direct current path 32 by the capacitor C6 in galvanically isapplied between the capacitor C6 and the gate G2 of the secondtransistor T2. It is therefore possible to apply a direct voltage to thegate G2 of the second transistor T2.

FIG. 6 illustrates a circuit diagram of an electronic circuit inaccordance with a modified embodiment of the second embodiment. Asillustrated in FIG. 6, the first resistor R1 is coupled between the nodeN4 and the distributed parameter line L3. The second resistor R2 iscoupled between the node N4 and the distributed parameter line L2. Thereare no resistors between the node N4 and the source S3. The otherstructure is the same as FIG. 5A of the second embodiment. Therefore,explanation of the other structure is omitted. In this way, the firstresistor R1 may be coupled between the node N4 and the drain D2 of thesecond transistor T2. The second resistor R2 may be coupled between thenode N4 and the drain D1 of the first transistor T1. It is thereforepossible to determine electrical potential of each transistor. The firstresistor R1 has only to be coupled between the node N2 and the node N4.The second resistor R2 has only to be coupled between the node N1 andthe node N4.

In the above-mentioned embodiments, a description is given of an FET(Field Effect Transistor) as the first transistor T1 through the thirdtransistor T3. However, the first transistor T1 through the thirdtransistor T3 may be a bipolar transistor. In this case, an emittercorresponds to the first terminal, a collector corresponds to the secondterminal, and a base corresponds to the control terminal. Thedistributed parameter line may be an inductance element such as aninductor. In the above-mentioned embodiments, a description is given ofa three-stage transistor structure. However, the present invention maybe applied to a four or more stage transistor structure. In theabove-mentioned embodiments, an amplifier circuit is described as anelectronic circuit. However, an electronic circuit other than theamplifier may be used.

“coupling from in high frequency” in the above-mentioned embodimentsmeans a coupling of a signal having a frequency included in a frequencyrange at which an electronic circuit can operate. “coupling ingalvanically” in the above-mentioned embodiments, means a coupling of asignal having a frequency that is sufficiently lower than the frequencyrange at which an electronic circuit can operate.

The present invention is not limited to the specifically disclosedembodiments and variations but may include other embodiments andvariations without departing from the scope of the present invention.

What is claimed is:
 1. An electronic circuit comprising: a firsttransistor having a control terminal to which a signal is input, a firstterminal, and a second terminal; a second transistor having a controlterminal coupled to the second terminal of the first transistor, a firstterminal, and a second terminal; a third transistor having a controlterminal coupled to the second terminal of the second transistor, afirst terminal and a second terminal; a common coupling point coupled tothe second terminal of the first transistor; a first direct current pathcoupled between the common coupling point and the first terminal of thethird transistor; and a second direct current path that is differentfrom the first direct current path and coupled between the commoncoupling point and the first terminal of the second transistor.
 2. Theelectronic circuit as claimed in claim 1 further comprising: a firstresistor coupled in the first direct current path in series; and asecond resistor coupled in the second direct current path in series. 3.The electronic circuit as claimed in claim 2, wherein: a firstdistributed parameter line is provided in series with the first resistorin the first direct current path; and a second distributed parameterline is provided in series with the second resistor in the second directcurrent path.
 4. The electronic circuit as claimed in claim 1 furthercomprising: a capacitor provided between the second terminal of thesecond transistor and the control terminal of the third transistor; anda bias path of which one end is coupled to the first direct current pathand the other is coupled to between the capacitor and the controlterminal of the third transistor.
 5. An electronic circuit comprising: afirst transistor having a control terminal to which a signal is input, afirst terminal, and a second terminal; a second transistor having acontrol terminal coupled to the second terminal of the first transistor,a first terminal, and a second terminal; a third transistor having acontrol terminal coupled to the second terminal of the secondtransistor, a first terminal and a second terminal; a common couplingpoint coupled to the first terminal of the third transistor; a firstdirect current path coupled between the common coupling point and thesecond terminal of the second transistor; and a second direct currentpath that includes a path different from the first direct current pathand coupled between the common coupling point and the second terminal ofthe first transistor.
 6. The electronic circuit as claimed in claim 5further comprising: a first resistor coupled to between the commoncoupling point and the second terminal of the second transistor; and asecond resistor coupled to between the common coupling point and thesecond terminal of the first transistor.
 7. The electronic circuit asclaimed in claim 5 further comprising a first resistor coupled tobetween the common coupling point and the first terminal of the thirdtransistor.
 8. The electronic circuit as claimed in claim 6 furthercomprising: a first distributed parameter line coupled to between thecommon coupling point and the second terminal of the second transistor;and a second distributed parameter line coupled to between the commoncoupling point and the second terminal of the first transistor.
 9. Theelectronic circuit as claimed in claim 6, wherein the first directcurrent path applies a bias to the control terminal of the thirdtransistor.
 10. The electronic circuit as claimed in claim 5 furthercomprising a capacitor coupled to between the second terminal of thefirst transistor and the control terminal of the second transistor,wherein: the second direct current path includes a path coupling betweenthe capacitor and the second terminal of the first transistor; and abias separated from the second direct current path by the capacitor ingalvanically is supplied to between the capacitor and the controlterminal of the second transistor.